Sorry for the inconvenience. Since it has been a while when you posted this issue. I would like to know if you are still experiencing this issue. Looking at the screenshot i think you were using Cell data to convert those file. If you have an option to connect to Wifi or a strong network, i would request you to try again.
Let us know about your current experience with the combine option.
Sorry if I didn't understand your query correctly. And I assume you mean if you have started merging process and you wanted to stop it? If that is your question, the answer is, no, this can't be stopped.
Also, if you want to delete some files from your Cloud account, you can go to https://documentcloud.adobe.com/ login with your Adobe ID and password. And you can manage your files there as well.